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Atmospheric Circulation and Weather Systems

Atmospheric Circulation and Weather Systems

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Study Action Plan (Sorted by Difficulty)
Air Masses and Fronts
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Atmospheric Pressure and Wind Systems
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ENSO and its Global Impact
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Extra Tropical and Tropical Cyclones
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Forces Affecting Wind Velocity and Direction
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General Atmospheric Circulation
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Local Wind Systems
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Vertical and Horizontal Pressure Variations
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Learning Objectives

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Learning Objectives

  • Understand the causes of atmospheric pressure differences and their role in atmospheric circulation and weather disturbances, including tropical storms.
  • Examine vertical and horizontal variations in atmospheric pressure and their influence on wind direction and velocity.
  • Analyze the effects of pressure gradient force, frictional force, and Coriolis force on wind velocity and direction, including the formation of geostrophic winds and cyclonic circulations.
  • Describe the global wind patterns driven by latitudinal heating variations, pressure belts, and Earth's rotation, including Hadley, Ferrel, and Polar cells.
  • Explore the formation and classification of air masses and the dynamics of fronts, including cold, warm, stationary, and occluded fronts.
  • Differentiate between extra tropical and tropical cyclones, their formation, structure, and impact, including the role of fronts and the Coriolis effect.
  • Explain local wind phenomena such as land and sea breezes, mountain and valley winds, and their impact on regional climates.
  • Discuss the El Nino-Southern Oscillation (ENSO) phenomenon, its causes, and its significant impact on global weather patterns and climate variability.

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Revision Notes & Summary

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Chapter Notes

Atmospheric Pressure and Wind Systems

  • Atmospheric Pressure: The weight of a column of air from the mean sea level to the top of the atmosphere, expressed in millibars (mb). At sea level, the average atmospheric pressure is 1,013.2 mb.
  • Wind: Air in horizontal motion, moving from high pressure to low pressure areas.
  • Weather Disturbances: Formed by the interaction of different air masses, leading to phenomena like tropical storms.

Vertical and Horizontal Pressure Variations

  • Vertical Pressure Variation: Pressure decreases rapidly with height, approximately 1 mb per 10 m increase in elevation.
  • Horizontal Pressure Variation: Studied using isobars, lines connecting places of equal pressure. Pressure systems include low-pressure (cyclones) and high-pressure (anticyclones) systems.

Forces Affecting Wind Velocity and Direction

  • Pressure Gradient Force: Causes wind to blow from high to low pressure areas.
  • Frictional Force: Affects wind speed, greatest at the surface.
  • Coriolis Force: Deflects wind due to Earth's rotation, to the right in the northern hemisphere and to the left in the southern hemisphere.
  • Geostrophic Wind: Wind that blows parallel to isobars when pressure gradient force is balanced by Coriolis force.

General Atmospheric Circulation

  • Global Wind Patterns: Driven by latitudinal heating variations, pressure belts, and Earth's rotation.
  • Cells: Hadley, Ferrel, and Polar cells describe the circulation patterns in different latitudes.

Air Masses and Fronts

  • Air Masses: Large bodies of air with uniform temperature and humidity, classified by their source regions (e.g., maritime tropical, continental polar).
  • Fronts: Boundaries between different air masses, including cold, warm, stationary, and occluded fronts.

Extra Tropical and Tropical Cyclones

  • Extra Tropical Cyclones: Develop in mid and high latitudes, characterized by a clear frontal system.
  • Tropical Cyclones: Originate over warm tropical oceans, characterized by strong winds and heavy rainfall. Known as cyclones, hurricanes, typhoons, or willy-willies depending on the region.

Local Wind Systems

  • Land and Sea Breezes: Caused by differential heating of land and sea, leading to sea breezes during the day and land breezes at night.
  • Mountain and Valley Winds: Daytime upslope winds (valley breeze) and nighttime downslope winds (mountain breeze).

ENSO and its Global Impact

  • ENSO (El Nino-Southern Oscillation): A climatic phenomenon involving the warming of central Pacific Ocean waters, affecting global weather patterns, such as causing heavy rainfall in South America and droughts in Australia and India.
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Practice Test – MCQs, True/False

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Multiple Choice Questions

A.

Valley winds occur at night as cool air descends into the valley.

B.

Mountain winds occur during the day as warm air rises up the slopes.

C.

Valley winds occur during the day as warm air rises up the slopes.

D.

Mountain winds occur at night as warm air rises up the slopes.
Correct Answer: C

Solution:

Valley winds occur during the day as warm air rises up the slopes, while mountain winds occur at night as cool air descends into the valley.

Chapter Concept:

Local Wind Systems

A.

The absence of the Coriolis force at the equator.

B.

The presence of high pressure systems at the equator.

C.

The lack of sufficient sea surface temperature near the equator.

D.

The presence of strong vertical wind shear at the equator.
Correct Answer: A

Solution:

Tropical cyclones require the Coriolis force to develop their characteristic rotation, which is absent at the equator, preventing cyclone formation.

Chapter Concept:

General Atmospheric Circulation

A.

It involves air rising at the equator and sinking at 30° N and S.

B.

It involves air sinking at the equator and rising at the poles.

C.

It involves air moving directly from the poles to the equator.

D.

It involves air moving from the equator to the poles without sinking.
Correct Answer: A

Solution:

The Hadley cell is characterized by air rising at the equator due to convection and sinking at around 30° N and S, forming a circulation pattern.

Chapter Concept:

General Atmospheric Circulation

A.

Near the poles

B.

Near the equator

C.

Near the Tropic of Cancer

D.

Near the Arctic Circle
Correct Answer: B

Solution:

The ITCZ forms near the equator where the trade winds converge, leading to rising air and cloud formation.

Chapter Concept:

Atmospheric Pressure and Wind Systems

A.

Near the Earth's surface with high friction

B.

In areas with strong vertical pressure gradient

C.

In the upper atmosphere with negligible friction

D.

At the equator where Coriolis force is maximum
Correct Answer: C

Solution:

Geostrophic winds occur in the upper atmosphere where friction is negligible, allowing the pressure gradient force and Coriolis force to balance each other.

Chapter Concept:

Forces Affecting Wind Velocity and Direction

A.

Daily temperature variations

B.

Coriolis force

C.

Pressure gradient

D.

Differential heating of land and sea
Correct Answer: B

Solution:

Local wind systems like land and sea breezes are primarily influenced by differential heating of land and sea, daily temperature variations, and the resulting pressure gradients. The Coriolis force has a minimal impact on these local wind systems.

Chapter Concept:

Local Wind Systems

A.

Solar radiation

B.

Condensation process in cumulonimbus clouds

C.

Frictional force

D.

Geothermal energy
Correct Answer: B

Solution:

The energy that intensifies a tropical cyclone comes from the condensation process in cumulonimbus clouds.

Chapter Concept:

Extra Tropical and Tropical Cyclones

A.

The extra tropical cyclone absorbs the tropical cyclone, leading to a larger and more intense storm system.

B.

The tropical cyclone dissipates rapidly due to the cooler air associated with the extra tropical cyclone.

C.

The two cyclones merge, resulting in a new cyclone with characteristics of both systems.

D.

The tropical cyclone intensifies as it draws energy from the extra tropical cyclone's frontal system.
Correct Answer: B

Solution:

When a tropical cyclone approaches an extra tropical cyclone, the cooler air associated with the extra tropical cyclone can cause the tropical cyclone to dissipate rapidly. The interaction does not lead to the absorption or merging of the two systems, as their dynamics and energy sources differ significantly.

Chapter Concept:

Extra Tropical and Tropical Cyclones

A.

Due to the sinking of air that has cooled at higher altitudes.

B.

Due to the convergence of polar and tropical air masses.

C.

Due to the direct heating of the Earth's surface at these latitudes.

D.

Due to the presence of large oceanic gyres.
Correct Answer: A

Solution:

At approximately 30° N and S latitudes, air that has risen at the equator cools and sinks, creating high-pressure belts known as subtropical highs.

Chapter Concept:

General Atmospheric Circulation

A.

Floods in China

B.

Drought in India

C.

Formation of polar easterlies

D.

Heavy rainfall on the west coast of South America
Correct Answer: C

Solution:

The formation of polar easterlies is not directly related to ENSO, which primarily affects weather patterns in the Pacific and surrounding regions.

Chapter Concept:

ENSO and its Global Impact

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True or False

Correct Answer: True

Solution:

Tropical cyclones require warm ocean water to maintain their energy. Once they reach land, the moisture supply is cut off, leading to their dissipation.

Chapter Concept :

Extra Tropical and Tropical Cyclones

Correct Answer: False

Solution:

Tropical cyclones do not form at the equator because the Coriolis force is zero there, preventing the necessary rotational motion.

Chapter Concept :

Forces Affecting Wind Velocity and Direction

Correct Answer: True

Solution:

Geostrophic winds result from the balance between the pressure gradient force and the Coriolis force, causing the wind to flow parallel to the isobars.

Chapter Concept :

Forces Affecting Wind Velocity and Direction

Correct Answer: False

Solution:

ENSO significantly impacts South America, causing heavy rainfall on the arid west coast.

Chapter Concept :

ENSO and its Global Impact

Correct Answer: True

Solution:

When isobars are straight and there is no friction, the pressure gradient force is balanced by the Coriolis force, resulting in geostrophic winds that blow parallel to the isobars.

Chapter Concept :

Atmospheric Pressure and Wind Systems

Correct Answer: False

Solution:

In the northern hemisphere, the Coriolis force deflects wind to the right, not to the left.

Chapter Concept :

Atmospheric Pressure and Wind Systems

Correct Answer: True

Solution:

Extra tropical cyclones have a distinct frontal system and can form over land or sea, unlike tropical cyclones which form only over warm ocean waters.

Chapter Concept :

Extra Tropical and Tropical Cyclones

Correct Answer: True

Solution:

Extra tropical cyclones are characterized by a well-developed frontal system, whereas tropical cyclones do not have such a system.

Chapter Concept :

Extra Tropical and Tropical Cyclones

Correct Answer: True

Solution:

The vertical pressure gradient force is much larger than that of the horizontal pressure gradient but is generally balanced by a nearly equal but opposite gravitational force, hence preventing strong upward winds.

Chapter Concept :

Vertical and Horizontal Pressure Variations

Correct Answer: True

Solution:

The vertical pressure gradient force is indeed larger than the horizontal pressure gradient force, and it is balanced by the gravitational force, which is why we do not experience strong upward winds.

Chapter Concept :

Vertical and Horizontal Pressure Variations

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